ES2775609T3 - A procedure for stabilizing a condensed phase composition including a cyclic ester in a polyester or lactide manufacturing process - Google Patents

Abstract

A process for stabilizing a condensed phase composition, containing i) at least one polymerizable cyclic ester and ii) at least one catalyst capable of catalyzing a cyclic ester polymerization and / or at least one initiator capable of initiating a cyclic ester polymerization and / or a reaction product or a residue of the at least one catalyst and / or of the at least one initiator, i) where the process is used in a process of manufacturing a polyester from a cyclic ester monomer and comprises the following steps of: a) providing a cyclic ester, b) polymerizing the cyclic ester in the presence of the catalyst and optionally the initiator in a reactor to form a reaction mixture comprising unreacted polyester and cyclic ester, c) subjecting the reaction mixture to devolatilization to obtain a purified polyester as a molten residue and a vapor, which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or the at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator, and d) subjecting the vapor stream to a condensation to obtain the composition of the condensed phase, where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture and / or to the composition of the condensed phase in an amount such that the degree of conversion of the polymerizable cyclic ester in the composition of the condensed phase is not more than 15% , where degree of conversion is 100 (c0 - CF) / C0, where c0 is the initial concentration of the cyclic ester in the condensed phase composition obtained by the condensation of the vapor stream and cF is the concentration of the cyclic ester in the composition of the condensed phase after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as initiator of the composition of the condensed phase and a subsequent heat treatment of the condensed phase sada under inert atmosphere conditions for 12 hours at 160 ° C, where ia) at least a part of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition, and / or ib) at least a part of the polymerization inhibitor is added to the reaction mixture before step c), and where devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively, at a temperature above 220 ° C and at a pressure below 5 mbar, or ii) where the process is used in a process for manufacturing lactide from lactic acid and comprises the steps of: a) providing lactic acid, b) polycondensation of the acid lactic acid in a reactor to form a reaction mixture comprising a polylactic acid prepolymer, c) adding a catalyst to the reaction mixture and depolymerizing the reaction mixture, d) devolatilizing the reaction mixture to obtain a stream crude lactide tea, e) subjecting the vapor stream to a condensation to obtain the condensed phase composition, where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture and / or to the condensed phase composition in a amount such that the degree of conversion of the polymerizable cyclic ester in the condensed phase composition is not more than 15%, where degree of conversion is 100 (c0 - CF) / C0, where c0 is the initial concentration of the cyclic ester in the condensed phase composition obtained by the condensation of the vapor stream and cF is the concentration of the cyclic ester in the condensed phase composition after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as an initiator of the condensed phase composition and a subsequent heat treatment of the condensed phase under inert atmosphere conditions for 12 hours at 160 ° C, where at least a part of the inhibitor of p olimerization is added to the vapor stream extracted from devolatilization and / or to the condensed composition.

Description

DESCRIPTION

A process for stabilizing a condensed phase composition including a cyclic ester in a polyester or lactide manufacturing process

The present invention relates to a process for stabilizing a condensed phase composition, containing i) at least one polymerizable cyclic ester and ii) at least one catalyst capable of catalyzing the polymerization of the cyclic ester and optionally at least one initiator capable of initiating the polymerization of the cyclic ester in a process for making a polyester from cyclic ester monomer or in a process for making lactide from lactic acid. Furthermore, the present invention relates to a condensed phase composition obtainable with such a process and to the use of such a condensed phase composition.

Cyclic esters, such as lactide, glycolide, lactones, or the like, are generally very sensitive to hydrolysis, which occurs in the presence of very low amounts of water. Hydroxyl and / or carboxyl groups, which are formed by the hydrolysis reaction, or any other substance containing hydroxyl and / or carboxyl groups, which may be present as impurities in the system, can act as polymerization initiators, especially in presence of even very low amounts of catalyst. Depending on the type of reaction mechanism, in fact, both alcohols and acids can act as initiators in ring-opening reactions, as reported in "Ring-opening polymerization manual", Dubois, Coulembier, Raquez, Wiley -VCH, 2009 Weinheim. Furthermore, when an initiator and a catalyst, such as an organometallic compound, are present in the system, the cyclic ester polymerization rate can be even further improved. Examples have been reported by Zhang et al. in Journal of Polymer Science-A, 1994, 32, 2965-2970 and by Kowalski et al. in Macromolecules, 2000, 33, 7359-7370.

Even partial polymerization of cyclic esters, such as lactide, glycolide, lactone or the like, in the presence of very low amounts of the above-mentioned initiators and / or catalysts leads to an increase in the viscosity of the composition or even to a solidification of the composition.

An example, in which a cyclic ester is used as a starting material, is a process for the polymerization of the cyclic diester of a hydroxyalkanoic acid into the respective polyhydroxyalkanoic acid. Specific examples for such polymers and cyclic esters resulting from their polymerization are lactide, which is the cyclic diester of lactic acid, which leads after polymerization to polylactic acid, glycolide, which is the cyclic diester of glycolic acid, which leads after polymerization to the polyglycolide, £ -caprolactone, which is the cyclic monoester of 6-hydroxyhexanoic acid, which leads after polymerization to polycaprolactone. These polymers are of particular interest as they are made from renewable resources and are biodegradable. Furthermore, the technological properties of these polymers are quite close to those of polymers derived from fossil-based resources, which is why these polymers are considered highly promising substitutes for the latter.

For example, polylactic acid has a wide range of applications, in the biomedical field, namely, e.g. g., in surgical implants, in films, such as eg. eg, in packaging, in fibers, such as eg. For example, for clothing, hygiene items, rugs and disposable plastic products, such as eg. eg, cutlery or disposable containers. Furthermore, polylactic acid has found wide application in composite materials, such as fiber reinforced plastics.

In general, two alternative methods are known for synthesizing polylactic acid. The first procedure is the direct polycondensation of lactic acid to polylactic acid, which leads to a low molecular weight polymer only. The second process is the ring-opening polymerization of lactide, which is the preferred process today for the industrial production of polylactic acid. The starting material of the last mentioned process, namely lactide, is commonly produced by fermenting carbohydrates from biomass, such as starch, sugar or corn resulting in lactic acid, by subsequent oligomerization of lactic acid and then subjecting the oligomers to a depolymerization reaction to obtain lactide. After purification, the lactide is polymerized in the presence of a catalyst and optionally an initiator to form high molecular weight polylactic acid. Unreacted lactide must be removed after polymerization to a final concentration of less than at least 0.5% by weight, to obtain a marketable grade product. Such removal of unreacted lactide can be achieved by means of at least one devolatilization step carried out at elevated temperature and reduced pressure. For example, a two-stage devolatilization process can be carried out to obtain the required degree of lactide removal and thus obtain a polymer having the required quality. To stop the polymerization reaction, an inhibitor is generally added to the polymeric product at the end of the polymerization and before or after the first devolatilization step. To maximize the yield of the polymeric product per lactide feed amount, generally the unreacted lactide is recovered after devolatilization, e.g. For example, by condensation, then optionally the condensed product is purified and then the condensed product is recycled in the polymerization reaction.

US 5,770,682 describes a process for preparing a polylactic acid comprising the steps of i) carrying out a ring-opening polymerization of lactide in the presence of a catalyst for the ring-opening polymerization of lactide to polylactic acid , ii) adding a compound capable of inactivating the catalyst to the resulting reaction mixture and iii) reducing the pressure in a reactor containing the reaction mixture and / or allowing an inert gas to pass through the reactor to remove unchanged lactide from polylactic acid by devolatilization, where the compound capable of inactivating the catalyst is preferably selected from the group consisting of phosphoric acid, phosphorous acid, derivatives thereof, and compounds. of aluminum. Two subsequent devolatilization steps are performed and the lactide-enriched vapor streams are recycled to the polymerization reactor. However, in this procedure, the non-purified lactide is returned to the polymerization reactor, so that impurities, such as by-products, as well as the polymerization catalyst and polymerization initiator that can be devolatilized along with the lactide, also they are recycled back to the reactor and enriched in the reaction mixture in an uncontrollable manner.

WO 2012/110117 A1 describes a similar process for preparing a polylactic acid which however makes use of a purification of the recycled lactide stream by crystallization. More specifically, the process described in WO 2012/110117 A1 comprises the steps of i) performing a ring-opening polymerization of lactide using a catalyst and a catalyst killer compound or a topcoat additive to obtain a crude polylactic acid having a weight average molecular weight (Mw) of at least 10,000 g / mol, ii) purifying the crude polylactic acid by removing and separating the low-boiling compounds comprising lactide and impurities from the crude polylactic acid by devolatilizing the low-boiling compounds as a gas phase stream, iii) purifying the lactide from devolatilization and removing impurities from the gas phase stream of evaporated low-boiling compounds by means of crystallization, where the lactide is purifies and impurities removed include a catalyst residue and a compound containing at least one g hydroxyl group in such a way that the purified lactide is then polymerized by reintroducing it into the ring opening polymerization reactor.

While the polymerization reactor and devolatilization apparatus operate continuously in these processes, the crystallization unit for purifying the lactide stream generally operates in batches. This means that the lactide must be collected after devolatilization, e.g. g., by condensation, and then stored in tanks in its liquid state (i.e. at elevated temperature) for a certain amount of time, i.e. generally for several days, before being fed into the unit. batchwise crystallization after a sufficient and desired amount of lactide has been collected. However, due to the long storage time at a relatively high temperature, certain problems can arise. First, the hot lactide can be oligomerized or partially polymerized, as a consequence of which the viscosity of the condensed composition comprising the lactide increases and the lactide to be recycled in the polymerization reactor is consumed. If a certain degree of oligomerization and / or polymerization of the condensed composition occurs, the viscous composition can no longer or at least cannot be easily processed in the crystallization unit. Second, the hot lactide can be completely oligomerized or polymerized, as a consequence of which the production cycle must be stopped and the condenser tank or other container, in which the liquid lactide was previously stored, must be tediously emptied or even replaced. by new equipment, because it is no longer possible to remove the solid polymer formed during plant operation. In order to at least reduce the probability of the aforementioned problems occurring, the condenser can be equipped with an internal heater, which can melt the oligomer and / or polymer possibly formed during storage. This allows unwanted highly viscous material to be melted and removed from the condenser in the event of unwanted oligomerization and / or polymerization. However, this solution is expensive and does not avoid the risk of unwanted oligomerization and / or polymerization of the lactide stream.

Another example is the process to produce lactide itself by depolymerizing an oligomer and / or polymer of lactic acid. Such a process typically comprises the steps of i) polymerizing lactic acid by polycondensation in a reactor under reduced partial pressure of water to form a reaction mixture comprising a polylactic acid prepolymer, ii) adding a catalyst to the reaction mixture and depolymerizing the reaction mixture to lactide, subsequently iii) devolatilizing the reaction mixture to obtain a crude vapor lactide stream and then subjecting the vapor stream to condensation, to obtain a condensed phase lactide composition. The stream thus obtained may still contain small amounts of substances, such as catalyst and initiator, which can initiate undesired oligomerization or polymerization of the lactide, so that if the respective lactide composition in condensed phase is not immediately processed further, the aforementioned problems occur, namely, oligomerization or even polymerization of the lactide which results in an increase in viscosity or even a solidification of the composition.

The object underlying the present invention is to provide a process for reliably stabilizing a condensed phase composition, containing a polymerizable cyclic ester and a substance that initiates and / or catalyzes an oligomerization or polymerization of the cyclic ester, in a manufacturing process of a polyester from cyclic ester monomer or in a lactide manufacturing process from lactic acid, thus reliably avoiding an unwanted reaction, in particular oligomerization or polymerization, of the cyclic ester and thus a unwanted consumption of the cyclic ester and an unwanted increase in viscosity or even solidification of the condensed phase composition, but still allowing the stabilized condensed phase composition to be used in its intended application.

According to the present invention, this object is fulfilled by providing a process for stabilizing a condensed phase composition, containing i) at least one polymerizable cyclic ester and ii) at least one catalyst capable of catalyze a polymerization of the cyclic ester and / or at least one initiator capable of initiating a polymerization of the cyclic ester and / or a reaction product or a residue of the at least one catalyst and / or of the at least one initiator,

i) in which the process is used in a process for manufacturing a polyester from a cyclic ester monomer and comprises the steps of:

a) provide a cyclic ester,

b) polymerizing the cyclic ester in the presence of the catalyst and optionally the initiator in a reactor to form a reaction mixture comprising unreacted polyester and cyclic ester,

c) subjecting the reaction mixture to devolatilization to obtain a purified polyester as a molten residue and a vapor, which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or the at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator, and

d) subjecting the vapor stream to condensation to obtain the composition of the condensed phase,

where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture and / or to the composition of the condensed phase in an amount such that the degree of conversion of the polymerizable cyclic ester in the composition of the condensed phase is not more than 15 %, where the degree of conversion is 100 ■ (c ⁰ - Cf) / C ⁰ , where c ⁰ is the initial concentration of the cyclic ester in the composition of the condensed phase obtained by the condensation of the vapor stream and cf is the concentration of the cyclic ester in the composition of the condensed phase after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as initiator of the composition of the condensed phase and a subsequent heat treatment of the condensed phase under inert atmosphere conditions for 12 hours at 160 ° C,

where

ia) at least a part of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition, and / or

ib) at least a part of the polymerization inhibitor is added to the reaction mixture before step c), and where devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively , at a temperature higher than 220 ° C and / or a pressure lower than 5 mbar, or

ii) where the process is used in a lactide manufacturing process from lactic acid and comprises the steps of:

a) provide lactic acid,

b) polycondensation of lactic acid in a reactor to form a reaction mixture comprising a polylactic acid prepolymer,

c) adding a catalyst to the reaction mixture and depolymerizing the reaction mixture,

d) devolatilizing the reaction mixture to obtain a crude lactide stream,

e) subjecting the vapor stream to condensation to obtain the condensed phase composition,

where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture and / or to the composition of the condensed phase in an amount such that the degree of conversion of the polymerizable cyclic ester in the composition of the condensed phase is not more than 15 %, where the degree of conversion is 100 ■ (c ⁰ - Cf) / Cü, where c ⁰ is the initial concentration of the cyclic ester in the composition of the condensed phase obtained by the condensation of the vapor stream and cf is the concentration of the cyclic ester in the composition of the condensed phase after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as initiator of the composition of the condensed phase and a subsequent heat treatment of the condensed phase in inert atmosphere conditions for 12 hours at 160 ° C,

where at least a part of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition.

The core of the present invention is to add much of a preferably highly effective inhibitor so that an oligomerization or polymerization of the cyclic ester included in the condensed phase composition is completely and reliably avoided, regardless of the amount of compounds capable of initiating and / or catalyze an oligomerization or polymerization of the cyclic ester are included in the condensed phase, regardless of the pressure and temperature conditions, in which the composition of the condensed phase is incubated, and regardless of the time, during which the composition of the condensed phase is incubated under these conditions. This solution is somewhat illogical, because a compound, namely a polymerization inhibitor, is added as an impurity in the cyclic ester composition, which will be purified from such impurities and, at least for some applications, which will be returned to a polymerization reactor to polymerize the cyclic ester composition, for which a polymerization inhibitor is of course , highly disadvantageous. However, the process according to the present invention reliably stabilizes a condensed phase composition derived from the devolatilization step and mainly includes polymerizable cyclic ester and catalyst and / or initiator to polymerize the cyclic ester and / or a reaction product or a residue of the at least one catalyst and / or at least one initiator and therefore reliably avoids the risk of oligomerization or polymerization of the cyclic ester composition leading to an undesired increase in viscosity or even unwanted solidification. desired effect of the cyclic ester composition, which makes the composition only difficult or not at all transportable in industrial plants, and further reliably prevents unwanted consumption of the cyclic ester, without avoiding the intended subsequent use of the phase composition stabilized condensed phase, such as the polymerization of the stabilized condensed phase composition after a certain incubation at elevated temperature for a long time. Therefore, on the one hand, unwanted consumption of the cyclic ester is avoided and, on the other hand, the viscosity of the condensed composition comprising cyclic ester is kept to a low degree so that the condensed composition can flow freely, and thus therefore, it can be easily transported in a production plant from one plant device to another. The polymerization inhibitor can be added to the condensed phase composition after the devolatilization step or, in a respective larger amount, which compensates for the loss during devolatilization, before the devolatilization step, when devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively, at a temperature higher than 220 ° C and / or a pressure lower than 5 mbar. The stabilized condensed phase of the cyclic ester composition can be purified, for example, by crystallization, to remove all impurities, including added polymerization inhibitor, immediately before further use, for example, in a polymerization reaction, or even can be used in non-purified form.In the latter case, if used in a polymerization reaction, only an excess of catalyst and / or initiator of the polymerization reaction can be added, which compensates for the amount of polymerization inhibitor present in the composition. Alternatively, even in the latter case, it can be mixed with a composition in liquid phase composed mainly or partially of fresh cyclic ester, still unreacted and free of inhibitors.

According to the present invention, a condensed phase composition is a liquid composition obtained after condensation of a gas phase.

Furthermore, a polymerization product of a cyclic ester is, according to the present invention, a molecule comprising at least ten molecules that formally result from the ring-opening polymerization of a cyclic ester, covalently connected to each other, while a product of oligomerization of a cyclic ester is, according to the present invention, a molecule comprising at least two to nine molecules that formally result from the opening of the ring of a cyclic ester covalently connected to each other.

The present invention is not specifically limited with respect to the melting point of the condensed phase composition, as long as it is less than 150 ° C. Preferably, the melting point of the condensed phase composition is between -50 ° C and below 130 ° C, more preferably -30 ° C and 120 ° C and even more preferably -10 ° C and 110 ° C. It is clear that the melting point of the condensed phase composition, consisting essentially of the cyclic ester and small amounts of polymerization initiator and / or catalyst, corresponds essentially to that of the cyclic ester. L-lactide, for example, has a melting point of between 95 ° C and 97 ° C, while £ -caprolactone has a melting point of -1.5 ° C and glycolide has a melting point of between 82 ° C and 83 ° C.

Preferably, the degree of conversion of the polymerizable cyclic ester in the condensed phase composition is not more than 10%, where the degree of conversion is, as indicated above, 100 ■ (c ⁰ - Cf) / Cü, where c ⁰ is the initial concentration of the cyclic ester in the composition of the condensed phase obtained by condensation of the vapor stream and cf is the concentration of the cyclic ester in the composition of the condensed phase after the addition of 150 ppm of octoate of tin as catalyst and 100 mmol / kg of ethylhexanol as initiator of the condensed phase composition and a subsequent heat treatment of the condensed phase composition under inert atmosphere conditions for 12 hours at 160 ° C. More preferably, the degree of conversion of the polymerizable cyclic ester in the condensed phase composition is not more than 5%, more preferably not more than 2%, still more preferably not more than 1% and still more preferably not more than 0.1 %.

Furthermore, it is preferred that the viscosity of the condensed phase composition at 110 ° C is between 0.1 and 500 mPa s, more preferably between 0.5 and 50 mPa ■ s and even more preferably between 1 and 20 mPa ■ s, where the viscosity is measured, according to the present invention, by using a suitable viscometer or rheometer, which is suitable for measuring the viscosity of liquid substances at high temperature. As an example, the viscosity can be measured with a rheometer (for example Antoon Paar Physica MCR 301) using a coaxial cylinder measuring system (for example according to DIN 54453 or according to ISO 3219), under rotating conditions at a speed of cut between 1 / s and 10 / s. Preferably, when measuring hot liquids, the rheometer is equipped with a pressurized cell (eg by nitrogen overpressure) that protects the condensed phase from the environment and prevents evaporation and loss of material during measurement. In other words, the composition of the condensed phase is at 110 ° C a free-flowing liquid or molten material, respectively, with a viscosity similar to a liquid.

Also with regard to the chemical nature of the cyclic ester, the two embodiments ia) and ib) of the present invention are not particularly limited, as long as it has the required melting point as specified above.

In particular, any cyclic monoester, any cyclic diester, any cyclic triester or the like can be used.

A particularly suitable cyclic monoester is β-caprolactone, while preferred examples of cyclic diesters are lactide, L-lactide, D-lactide, meso-lactide, glycolide, and mixtures thereof. Therefore, the at least one cyclic ester is preferably selected from the group consisting of lactide, L-lactide, D-lactide, mesolactide, £ -caprolactone, glycolide, or mixtures of one or more of the substances mentioned above.

As indicated above, the composition of the condensed phase resulting from the devolatilization of the reaction mixture containing i) the at least one polymerizable cyclic ester, ii) the at least one catalyst and optionally the at least one initiator and iii) a oligomerization and / or polymerization product of the cyclic ester and the subsequent condensation of the vapor stream extracted from devolatilization is a stream that mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or the least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator. Usually, the condensed phase composition includes at least 80% by weight, more preferably more than 90% by weight and even more preferably more than 95% by weight of the polymerizable cyclic ester.

There is no particular limitation of the present patent application with respect to the chemical nature of the catalyst included in the reaction mixture and in the condensed phase composition and this depends, of course, on the type of pretreatment of the reaction mixture. Preferably, the reaction mixture and the condensed phase composition preferably each contain as a catalyst at least one organometallic compound comprising a metal selected from the group consisting of magnesium, titanium, zinc, aluminum, indium, yttrium, tin, lead, antimony , bismuth and any combination of two or more of the metals mentioned above, wherein the at least one organometallic compound preferably comprises as an organic residue a residue selected from the group consisting of alkyl groups, aryl groups, halides, oxides, alkanoates, alkoxides and any combination of two or more of the groups mentioned above.

Halides, oxides, alkanoates, alkoxides of the abovementioned metals, as well as compounds containing alkyl or aryl groups of these metals are particularly preferred catalysts. Even more preferred polymerization catalysts are in this case tin octoate, that is to say tin (II) -2-ethylhexanoate. These catalysts are particularly preferred for the case of alternatives ia) and ib), when the cyclic ester of the condensed phase composition is lactide, and for alternative ii).

Usually, the reaction mixture and optionally the condensed phase composition contains from 0.0001 to 1% by weight and preferably from 0.001 to 0.05% by weight of the amount of catalyst, while in the case of organometallic compounds the amount of metal in the reaction mixture, as well as in the condensed phase composition is preferably 0.1 to 200 ppm and more preferably 1 to 50 ppm.

Preferably, in addition to a polymerization catalyst, the reaction mixture and optionally the condensed phase composition includes a polymerization initiator or a polymerization co-catalyst, respectively, as well as possible reaction products or residues of the catalyst and initiator. Usually, the reaction mixture, as well as the composition of the condensed phase, each contain as initiator at least one compound comprising at least one carboxyl group and / or hydroxyl group, which are very effective in initiating the oligomerization of cyclic esters. Preferably, the reaction mixture and optionally the condensed phase composition includes as a polymerization initiator at least one compound selected from the group consisting of water, alcohols, lactic acid, oligomers of the cyclic ester, polymers of the cyclic ester, and any combination of two or more of the aforementioned substances. Preferably, the oligomer and / or polymer of the cyclic ester is an oligomer and / or polymer of lactic acid or glycolide.

Although a catalyst is defined within the scope of the present invention according to the usual definition of this term in the relevant field as a substance that increases the rate of a chemical reaction without being consumed by the reaction, a polymerization initiator or a co-catalyst polymerization or promoter, respectively, is defined, also according to the usual definition of this term in the relevant field, as a substance that enhances catalytic activity.

Usually, the reaction mixture contains an amount of initiator corresponding to 0.1 to 100 mmol and more preferably 1 to 40 mmol per kg of raw material.

The devolatilization of the reaction mixture including i) the at least one polymerizable cyclic ester, ii) the at least one catalyst and optionally the at least one initiator and / or a reaction product or a residue of the at least one catalyst and optionally of the at least one initiator and iii) an oligomerization and / or polymerization product of the cyclic ester, to produce the vapor stream, can be carried out in any known devolatilization reactor at elevated temperature and under reduced pressure. In alternatives ia) and ii) of the process according to the present invention, preferably, devolatilization is carried out at a temperature between 170 ° C and 250 ° C and at a pressure between 0.1 and 50 mbar, more preferably at a temperature between 180 ° C and 240 ° C and at a pressure between 0.5 and 25 mbar and most preferably at a temperature between 190 ° C and 230 ° C and at a pressure between 1 and 10 mbar. Although devolatilization can be done under vacuum, alternatively an inert gas, such as nitrogen, argon or carbon dioxide, can be purged through of the devolatilization device. The devolatilization conditions mentioned above are particularly useful for devolatilizing a reaction mixture that includes lactide as a cyclic ester, but they are also useful, for example, for devolatilizing a reaction mixture that includes glycolide or β-caprolactone as a cyclic ester. In alternative ib) of the process according to the present invention, devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively, at a temperature higher than 220 ° C and / or a pressure lower than 5 mbar. Preferably, devolatilization is carried out in alternative ib) at a temperature of 205 to 220 ° C and a pressure of less than 4 mbar and more preferably at a temperature of 205 to 220 ° C and a pressure of less than 3 mbar. For example, devolatilization can be carried out in alternative ib) at a temperature higher than 205 ° C and a pressure lower than 3 mbar or at a temperature higher than 210 ° C and a pressure lower than 4 mbar.

Furthermore, condensation can be carried out in any condensation device, in which the vapor stream extracted from the devolatilization device is condensed in the liquid phase by cooling it to a temperature above its melting point and below its boiling point. at the pressure at which the composition of the condensed phase condenses.

As a polymerization inhibitor, any substance within the scope of the present invention can be used, which can inhibit an oligomerization and / or polymerization of a cyclic ester, particularly in the presence of a catalyst and / or an initiator. Since the amount of polymerization inhibitor to be added to the reaction mixture and / or condensed phase composition decreases with the effectiveness of the polymerization inhibitor, it is preferred to use a strong polymerization inhibitor. In particular, good results are achieved when the at least one polymerization inhibitor is an imine or a diimine, such as N, N'-bis (salicylidene) -1,3-propanediamine and / or a phosphoric acid derivative, such as as a phosphoric acid ester, preferably an alkanoic acid phosphate or an alkoxylated alcohol-based acid phosphate compound, more preferably a stearic acid phosphate compound and most preferably a mono-C4-18 alkyl phosphate ester, a di-C4-18 alkyl phosphate ester or a mixture of mono-stearic acid phosphate and di-stearic acid phosphate.

According to the present invention, the term polymerization inhibitor is defined, in harmony with its usual definition in the relevant field, as an agent, which inhibits the action of a polymerization catalyst and a polymerization initiator, and therefore, it inhibits a cyclic ester polymerization in the presence of a polymerization catalyst and a polymerization initiator.

In a further development of the present invention, it is suggested that the amount of the polymerization inhibitor in the condensed phase composition is 0.001 to 0.5% by weight based on the total weight of the composition. More preferably, the amount of the polymerization inhibitor in the condensed phase composition is from 0.01 to 0.2% by weight and most preferably from about 0.02 to 0.15% by weight based on the total weight of the composition. The last mentioned amounts are particularly suitable, if a strong polymerization inhibitor is used, such as an imine or a diimine and / or a phosphoric acid derivative, such as a phosphoric acid ester, preferably an alkanoic acid phosphate or a compound. of alkoxylated alcohol-based acid phosphate, more preferably a stearic acid phosphate compound and most preferably a mono-C4-18 alkyl phosphate ester, a di-C4-18 alkyl phosphate ester or a mixture of phosphate of monostearic acid and di-stearic acid phosphate.

According to a particularly preferred embodiment of the present invention, the process for stabilizing a condensed phase composition according to the present invention used in a process for manufacturing polyester from cyclic ester monomer is carried out according to alternative ia), that is, to that the procedure includes the stages of:

a) provide a cyclic ester,

b) polymerizing the cyclic ester in the presence of a catalyst and optionally an initiator in a reactor to form a reaction mixture comprising polyester and unreacted cyclic ester,

c) subjecting the reaction mixture to devolatilization to obtain a purified polyester as the molten residue and steam, which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator, and

d) subjecting the vapor stream to condensation to obtain the condensed phase composition,

where at least a part of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition.

In this embodiment, the polymerization inhibitor is added directly to the vapor stream extracted from devolatilization and / or to the condensed composition, respectively. Due to the addition of the polymerization inhibitor after devolatilization, i.e. to the vapor stream extracted from devolatilization or to the condensed composition, a comparable low amount of polymerization inhibitor must be added, i.e. exactly that amount, which is necessary, to avoid oligomerization and / or polymerization of the cyclic ester included in the condensed phase composition, even after long-term storage in molten form at an elevated temperature.

In order to be able to work with the minimum amount of polymerization inhibitor to sufficiently stabilize the condensed phase composition, it is suggested in a further development of the present invention to mix the condensed phase composition during and preferably also after the addition of the polymerization inhibitor in the condensed phase composition. In this way, a homogeneous distribution of the polymerization inhibitor in the condensed phase composition is ensured, so that only a minimal amount of it must be added to the condensed phase composition. In contrast to this, if any inhomogeneity arises throughout the composition of the condensed phase, more than a minimal amount of the polymerization inhibitor would be necessary to ensure that also in those places of the composition of the condensed phase that have the lower inhibitor concentration, there is sufficient inhibitor to reliably suppress oligomerization or polymerization of the condensed phase composition.

The mixing can be carried out either in the vapor phase or in the final composition of the condensed phase, by any known mixer, which can ensure a homogenizing mixture. In particular, any suitable static mixer and / or any suitable dynamic mixer can be used. Particularly good results are obtained using a mixer selected from the group consisting of SMI, SMV ™, KVM, SMX ™, SMX ™ plus or SMXL ™ Sulzer static mixers, of dynamic mixers equipped with impellers or helical belts, of anchor mixers , as well as any combination of two or more of the mixers mentioned above.

The amount of the polymerization inhibitor included in the condensed phase composition is, in the aforementioned embodiment, the same as that described above.

This embodiment is particularly useful for making a polylactic acid, a polycaprolactone or a polyglycolide, that is, to use a cyclic ester selected from the group consisting of lactide, L-lactide, D-lactide, meso-lactide, £ -caprolactone, and glycolide. .

As the polymerization catalyst and polymerization initiator, the above-mentioned substances can be used in the present embodiment in the amounts described above as preferred. Preferably, the reaction mixture of step b) includes 0.5 to 50% by weight and preferably 1 to less than 15% by weight of cyclic ester.

Furthermore, the devolatilization and condensation conditions described above as preferred can be used in the present embodiment.

Preferably, the polymerization is carried out in step b) of the process according to the present embodiment until a polymer having an absolute weight average molecular weight (Mw) of at least 10,000 g / mol, preferably of at least 15,000 g / mol and more is preferably obtained at least 20,000 g / mol. Mw is measured according to the present invention by gel permeation chromatography (GPC) using absolute calibration. Measurement is preferably performed on a Viscotek TADmax (Malvern) equipped with triple detection (refractive index, viscometer and right / low angle light scattering) using the solvent enhanced light scattering procedure, chloroform as polymeric solvent, acetone as eluent and calibration of equipment parameters performed with PMMA standards.

Furthermore, it is preferred that the polymerization is carried out in step b) at a temperature between 120 ° C and 250 ° C, more preferably at a temperature between 150 ° C and 200 ° C and most preferably at a temperature between 160 ° C. and 190 ° C.

Optionally, a polymerization inhibitor can be included in the aforementioned embodiment, in addition to the polymerization inhibitor, which is added to the vapor stream extracted from devolatilization and / or to the condensed composition, before step c), that is, before subjecting the reaction mixture to devolatilization to obtain a purified polyester as the molten residue and steam.

According to another embodiment of the present invention, the process for stabilizing a condensed phase composition according to the present invention used in a process for manufacturing polyester from cyclic ester monomer is carried out according to alternative ib), that is, so that the procedure includes the stages of:

a) provide a cyclic ester,

b) polymerizing the cyclic ester in the presence of a catalyst and optionally an initiator in a reactor to form a reaction mixture comprising polyester and unreacted cyclic ester,

c) subjecting the reaction mixture to devolatilization to obtain a purified polyester as the molten residue and steam, which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator, and

d) subjecting the vapor stream to condensation to obtain the composition of the condensed phase,

where at least a part of the polymerization inhibitor is added to the reaction mixture before step c), and where devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively, at a temperature higher than 220 ° C and / or a pressure lower than 5 mbar.

Because the polymerization inhibitor is added in this embodiment to the reaction mixture before step c), that is, before subjecting the reaction mixture to devolatilization to obtain a purified polyester as the molten residue and steam , which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or the at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least an initiator, a comparable high amount of polymerization inhibitor could be added, if not in addition to this, also after devolatilization, more polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition. This is due to the fact that, depending on the specific boiling point and volatility of the polymerization inhibitor, not all of the total amount of inhibitor added to the reaction mixture before step c) can be devolatilized in step d) and transferred to the condensed phase composition.

In this embodiment, devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively, at a temperature higher than 220 ° C and / or a pressure lower than 5 mbar The devolatilization conditions mentioned above they are particularly useful for devolatilizing a reaction mixture that includes lactide as a cyclic ester, but they are also useful, for example, for devolatilizing a reaction mixture that includes glycolide, β-caprolactone or mixtures thereof as a cyclic ester.

The amount of the polymerization inhibitor included in the reaction mixture before step c) is such that the content of the polymerization inhibitor in the composition of the subsequent condensed phase is in the aforementioned embodiment preferably 0.001 to 0.5% in weight based on the total weight of the composition. More preferably, the amount of the polymerization inhibitor in the condensed phase composition is from 0.01 to 0.2% by weight and most preferably from about 0.02% to 0.15% by weight based on the total weight. of the composition. The last mentioned amounts are particularly suitable, if a strong polymerization inhibitor, such as an imine or a diimine and / or a phosphoric acid derivative, such as a phosphoric acid ester, preferably an alkanoic acid phosphate or a phosphate compound is used. Alkoxylated alcohol based acid, more preferably a stearic acid phosphate compound and most preferably a mono-C4-18 alkyl phosphate ester, a di-C4-18 alkyl phosphate ester, or a mixture of acid phosphate monostearic and di-stearic acid phosphate. To achieve said appropriate polymerization inhibitor content, when devolatilization is carried out under the above-mentioned preferred conditions 0.001 to 0.5% by weight, more preferably 0.01 to 0.2% by weight and most preferably about 0.02 to 0.15% by weight based on the total weight of the polymerization inhibitor in the reaction mixture should in this embodiment be added to the reaction mixture before step c).

More specifically, preferably devolatilization in step c) is carried out in this embodiment at a temperature between more than 203 ° C and 300 ° C and at a pressure between 0.1 and less than 5 mbar, the polymerization inhibitor is selected from group consisting of imines or diimines, derivatives of phosphoric acid, such as phosphoric acid esters, alkanoic acid phosphate or alkoxylated alcohol-based acid phosphate compounds and mixtures comprising two or more of the substances mentioned above, and the Amount of the polymerization inhibitor added to the reaction mixture before step c) is 0.01 to 0.20% by weight based on the total weight of the reaction mixture.

More preferably, devolatilization in step c) is carried out in this embodiment at a temperature between 205 ° C and 220 ° C and at a pressure between 0.5 and less than 4 mbar, the polymerization inhibitor is selected from the group consisting of imines or diimines, phosphoric acid derivatives, such as phosphoric acid esters, alkanoic acid phosphate or alkoxylated alcohol-based acid phosphate compounds and mixtures comprising two or more of the substances mentioned above, and the amount of the inhibitor of polymerization added to the reaction mixture before step c) is 0.01 to 0.20% by weight based on the total weight of the reaction mixture.

Even more preferably, devolatilization in step c) is carried out at a temperature between 205 and 220 ° C and at a pressure between 1 and less than 3 mbar, the polymerization inhibitor is selected from the group consisting of diimines, acid esters phosphoric, alkanoic acid phosphate or ethoxylated alcohol-based acid phosphate compounds and mixtures comprising two or more of the substances mentioned above, and the amount of polymerization inhibitor added to the reaction mixture before step c) is 0.01 to 0.2% by weight based on the total weight of the reaction mixture.

In order to be able to work with the minimum amount of polymerization inhibitor to sufficiently stabilize the condensed phase composition, it is also suggested for this embodiment to perform a mixture already in the vapor phase or in the final condensed phase composition, by any known mixing procedure. as described above.

Furthermore, this embodiment is particularly useful for making a polylactic acid, a polycaprolactone or a polyglycolide, that is, to use a cyclic ester selected from the group consisting of lactide, L-lactide, D-lactide, meso-lactide, £ -caprolactone and glycolide and mixtures thereof.

As the polymerization catalyst and polymerization initiator, the above-mentioned substances can be used in the present embodiment in the amounts described above as preferred. Preferably, the reaction mixture of step b) includes 0.5 to 50% by weight and preferably 1 to less than 15% by weight of cyclic ester.

Furthermore, the condensation conditions described above as preferred can be used in the present embodiment.

Preferably, the polymerization is carried out in step b) of the process according to the present embodiment until a polymer is obtained having a Mw of at least 10,000 g / mol, preferably of at least 15,000 g / mol and more preferably of at least 20,000 g / mol.

Furthermore, it is preferred that the polymerization is carried out in step b) at a temperature between 120 ° C and 250 ° C, more preferably at a temperature between 150 ° C and 200 ° C and most preferably at a temperature between 160 ° C. and 190 ° C.

Optionally, a polymerization inhibitor can be included in the aforementioned embodiment, in addition to the polymerization inhibitor, which is added to the reaction mixture before step c), to the vapor stream extracted from devolatilization and / or to the composition. condensed.

In addition to using the composition in a process for manufacturing a polyester, the process for stabilizing a condensed phase composition according to the present invention can be used according to alternative ii) in a process for manufacturing a lactide from lactic acid, where the The method preferably comprises the steps of:

a) provide lactic acid,

b) polycondensation of lactic acid in a reactor to form a reaction mixture comprising a polylactic acid prepolymer,

c) adding a catalyst to the reaction mixture and depolymerizing the reaction mixture

d) devolatilizing the reaction mixture to obtain a crude lactide stream,

e) subjecting the vapor stream to condensation to obtain the composition of the condensed phase,

where at least a part, preferably all of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition. It is advantageous to add all the polymerization inhibitor to the vapor stream and / or condensed phase to minimize possible interference with the depolymerization step, particularly when carried out in a continuous process with continuous devolatilization.

A cyclic ester prepolymer is, according to the present invention, a molecule with a number average molecular weight of less than 10,000 g / mol.

Preferably, the prepolymerization step is carried out in step b) at a pressure of 1 to 300 mbar and a temperature of up to 250 ° C to dehydrate the lactic acid to a prepolymer with a degree of polymerization of about 7 to 20 and preferably of about 10. This prepolymerization can be carried out batchwise or continuously and preferably is carried out continuously.

In a further development of the present invention, it is suggested that the depolymerization in step c) be carried out continuously at a pressure of 1 to 10 mbar and a temperature of 150 ° C to 250 ° C, where the compounds are preferably used as catalyst mentioned above as a catalyst and in an amount as mentioned above.

Furthermore, the devolatilization and condensation conditions described above as preferred can be used in the present embodiment.

In a further development of the present invention, it is suggested that the amount of the polymerization inhibitor in the condensed phase composition is 0.001 to 0.5% by weight based on the total weight of the composition. More preferably, the amount of the polymerization inhibitor in the condensed phase composition is from 0.01 to 0.2% by weight and most preferably from about 0.02 to 0.15% by weight based on the total weight of the composition. The last mentioned amounts are particularly suitable, if a strong polymerization inhibitor is used, such as an imine or a diimine and / or a phosphoric acid derivative, such as a phosphoric acid ester, preferably an alkanoic acid phosphate or a compound. alkoxylated alcohol based acid phosphate, more preferably a stearic acid phosphate compound and most preferably a mono-C4-18 alkyl phosphate ester, a di-C4-i8 alkyl phosphate ester, or a mixture of monostearic acid phosphate and di-stearic acid phosphate.

In order to be able to work with the minimum amount of polymerization inhibitor to sufficiently stabilize the condensed phase composition, it is also suggested for this embodiment to mix the inhibitor directly into the vapor phase or into the condensed phase composition during and more preferably also after the condensation in step d), preferably using a mixer as described above.

According to a further particularly preferred embodiment of the present invention, the condensed phase composition comprising the polymerization inhibitor is subjected to a purification step, before being subjected to its intended use. During the purification step, impurities included in the condensed phase composition, such as the polymerization catalyst and / or the polymerization initiator, as well as the polymerization inhibitor, are removed. The condensed phase composition purified in this way consists at least essentially of the cyclic ester.

Preferably, the condensed phase composition comprising the polymerization inhibitor is subjected to a melt crystallization step, a distillation step or a solvent crystallization step, and preferably a melt crystallization step, to obtain a composition of purified condensed phase, before it is put to its intended use.

More preferably, the condensed phase composition comprising the polymerization inhibitor is subjected to a melt crystallization step, to obtain a purified condensed phase composition, before being subjected to its intended use. Preferably, the condensed phase composition is crystallized in the melt crystallization step without any solvent, which has the advantage that no additional steps are required to remove solvents.

Melt crystallization is preferably carried out by static crystallization, dynamic crystallization, or a combination thereof. For this purpose, any suitable type of static crystallizers and / or dynamic crystallizers known to a person skilled in the art can be used. A particular preferred example for a dynamic crystallizer is a falling film crystallizer.

Static crystallization can be performed using tubes that are heated or cooled by internal circulation of heat transfer medium or alternatively by use of plates, which can be oriented vertically, horizontally or in any preferred orientation, where the plates are suspended in the feed. molten that needs to be purified by crystallization. In a first step, the substance to be purified is crystallized on the surface of the vertical plates, where the remaining melt that predominantly includes impurities is removed as the first residue. In a second stage, the crystallized mass is partially melted or "sweated", respectively, to predominantly melt the remaining impurities included in the crystals and the resulting melt is removed as a second residue from the crystallizer. Then, in a third stage, the crystals thus purified are melted and removed as the product melts. Static crystallization has the advantage of high flexibility, wide operating range, easy operation since there is no glass sludge handling and no filtration, high reliability and low operating costs. In particular, static crystallization is preferred over dynamic crystallization when purifying thermally sensitive substances.

A falling film crystallizer consists of an essentially vertical tube system. During the crystallization process, the composition to be purified and the heat transfer medium flow as a falling film on the surfaces of the tubes. However, while the composition to be purified flows as a falling film on the inner surface of the tubes, the heat transfer medium used for cooling and heating is distributed to wet the outer surface of the tubes. During crystallization, cold heat transfer medium is used to cool the tubes, so that the substance to be purified crystallizes on the inner surface of the tubes, where the remaining melt that predominantly includes impurities is removed from the crystallizer. as the first residue. After crystallization, partial melting or "sweating" is induced, respectively, by slightly raising the temperature of the heat transfer medium, to predominantly melt the remaining impurities included in the crystals and the resulting melt is removed as a second residue from the crystalizer. The final melting of the crystals is then performed by applying higher temperatures to provide the purified liquid, which is removed as a molten product. Falling film crystallization leads to high capacity and is characterized by easy operation as there is no handling of the crystal suspension or filtration, by high reliability and by low operating costs.

Preferably, the crystallization is carried out by cooling the condensed phase composition to a temperature that is 0.1 to 50 ° C lower than the solidification point of the composition, and more preferably cooling the condensed phase composition to a temperature 0.5 to 25 ° C lower than the solidification point of the composition.

According to an alternative embodiment to that mentioned above, purification of the condensed phase composition is not carried out before it is subjected to its intended use. In this embodiment, the condensed phase composition is used in subsequent application, such as polymerization to polyester, such as polylactic acid, in non-purified form, wherein respective larger amounts of catalyst and initiator are added to account for the remaining polymerization inhibitor.

The intended use of the condensed phase composition may in particular be its recycling in a reactor, such as a polymerization reactor used for the production of polyester, such as polylactic acid, or in a prepolymerization reactor used for the production of prepolymer of polyester as a precursor for a depolymerization in a cyclic diester, such as lactide.

The reactor to which the composition of the condensed phase is recycled can in particular be a closed-loop reactor or a plug-flow reactor.

According to another specific aspect, the present invention relates to a process for stabilizing a condensed phase composition used in a process for manufacturing a polyester from a cyclic ester monomer, where the process preferably comprises the steps of:

a) provide a cyclic ester,

b) polymerizing the cyclic ester in the presence of a catalyst and optionally an initiator in a reactor to form a reaction mixture comprising polyester and unreacted cyclic ester,

c) subjecting the reaction mixture to devolatilization to obtain a purified polyester as the molten residue and steam, which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator, and

d) subjecting the vapor stream to condensation to obtain the composition of the condensed phase,

where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture before step c), and, where devolatilization is carried out at a temperature higher than 220 ° C and / or at a pressure lower than 5 mbar.

Preferably, devolatilization is carried out at a temperature between 220 ° C and 300 ° C and / or at a pressure between 1 and 5 mbar and more preferably at a temperature between 220 ° C and 250 ° C and / or at a pressure of between 1 and 3 mbar.

As the cyclic ester, catalyst and initiator, the compounds described above for the other embodiments can be used in the amounts mentioned above.

According to another aspect, the present invention refers to a plant for stabilizing a condensed phase composition used in a process for manufacturing a polyester from a cyclic ester monomer, in which the plant comprises:

a) at least one reactor for polymerizing cyclic ester in the presence of a catalyst and optionally an initiator to form a reaction mixture comprising unreacted polyester and cyclic ester,

b) at least one devolatilization device for separating a low-boiling vapor phase comprising cyclic ester and the catalyst and / or the initiator and / or a reaction product or a residue of the at least one catalyst and / or the less one initiator from a molten residue that primarily includes polymerized cyclic ester, and

c) at least one condenser device for condensing the vapor stream to a condensed phase composition,

wherein the plant further comprises at least one feed line to feed a polymerization inhibitor into the vapor stream extracted from devolatilization and / or into the condensed composition.

Preferably, the plant further comprises a mixer, which is located, e.g. eg, in the condenser or downstream of the condenser, which is adapted to homogeneously mix the polymerization inhibitor in the condensed phase composition. Preferably, the mixer is a mixer as described above. Alternatively, the mixer can be positioned so that mixing already takes place in the vapor phase.

Furthermore, it is preferred that the plant further comprises at least one purification device downstream of the condenser, which makes it possible to remove impurities and, in particular, polymerization catalysts, polymerization initiators and polymerization inhibitors of a cyclic ester that includes a phase composition. condensed. Preferably, the purification device is a static crystallizer, a dynamic crystallizer, or a combination thereof. For this purpose, any type of static crystallizers and / or dynamic crystallizers known to a person skilled in the art can be used. A particular preferred example for a dynamic crystallizer is a falling film crystallizer.

Preferably, the at least one purification device is connected to the condenser through a line and further comprises a return line leading from the purification device back to the reactor system.

According to a particular preferred embodiment of the present invention, the steam stream extracted from a devolatilization device is subjected to a washing step in a washing section of the plant. For example, the vapor stream drawn from a devolatilization device is led to a countercurrent column, which is preferably maintained under vacuum, and is contacted there with an aqueous solution, to dissolve and at least partially hydrolyze the lactide included in the steam stream. The resulting mixture is then preferably conducted to a heat exchanger, where it is heated to a temperature of, for example, 10 to 95 ° C and preferably 10 to 60 ° C, before being taken to a reactor, where it is maintained with a residence time of at least 0.1 to 30 minutes and preferably of at least 0.1 to 10 minutes at this temperature to allow complete or at least almost complete dissolution and hydrolysis of the lactide in the aqueous solution, before bringing it into to a further heat exchanger, where it is cooled to a temperature of, for example, 5 to 25 ° C, preferably 5 to 15 ° C, and more preferably 7 to 12 ° C. Subsequently, the cooled mixture is recycled as aqueous solution to the countercurrent column. A partial stream of the recirculated mixture is removed from any location in the recirculation system, such as prior to conducting the mixture to the first heat exchanger, and then removed.

It has been found during the present invention that, in such wash sections, conventional phosphate-based polymerization inhibitors, such as monostearic acid phosphates and di-stearic acid phosphates and mixtures thereof, often cause fouling problems of the washing section. Such fouling can cause line blockage and solid debris, which can undesirably accumulate within the wash section as an insoluble fraction. Without wishing to be limited to any particular mechanism, it is considered that this fouling is caused by devolatilization of the polymerization inhibitors and / or their degradation products and that these are insoluble in the acidic aqueous solution present in the wash section.

One possible approach to solve this problem is to use a phosphate-based polymerization inhibitor that is liquid at room temperature and also highly volatile, such as dibutyl phosphate, which is a liquid at room temperature with a boiling point of 275, 3 ° C at 760 mmHg, and therefore highly volatile under vacuum conditions as used in such wash sections. It was considered that such volatile phosphate-based polymerization inhibitors and / or their degradation products when transferred together with the gas stream at the outlet of a devolatilization vessel to the scrubbing section, would be easily devolatilized there and hence Therefore, they would not cause fouling in the washing section and the downward recirculation system. Alternatively, the fraction of inhibitor and / or degradation products that could be transferred to the washing section and not easily devolatilized there, would be there in a liquid state, therefore again without causing any fouling in the parts of the washing section. washed. However, after testing, it was found in the present invention that, although scale did not occur in the portion of the wash section with such highly volatile polymerization inhibitors, surprisingly significant scale did occur in the first and / or second ascending devolatilization chambers. Such fouling leads to the formation of a dark-colored insoluble solid coating on the surface of said chambers. Depending on the production time, the color of the resulting polyester polymer product also deteriorates as fouling progresses. Again, without wishing to be subject to any particular mechanism, this fouling is considered to be caused by the vapor phase thermal degradation of such highly volatile phosphate-based polymerization inhibitors within the chamber to give a solid residue in the cells. chamber surfaces.

Surprisingly, it was subsequently discovered that these fouling problems both in the devolatilization chambers and their downstream wash sections to remove an ester from the steam and recirculation to reduce the ester content can be alleviated by the use of a polymerization inhibitor, either a diimine, such as N, N'-bis (salicylidene) -1,3-propanediamine (CAS No. 120-70-7), or a phosphate ester according to the general formula (I) described below. Again, without wishing to be bound by any particular mechanism, these phosphate esters are considered to alleviate these fouling problems in devolatilization chambers by being sufficiently high in molecular weight, and therefore non-volatile, by controlling lengths. chain from the remains. Furthermore, by imparting hydrophilicity to the phosphate ester through the general polar structure as in the general formula (II) below, the phosphate ester and / or its degradation products are sufficiently hydrophilic and therefore soluble in aqueous solutions. acid to avoid incrustation problems in the washing section and its recirculation system. Furthermore, such diimines, such as N, N'-bis (salicylidene) -1,3-propanediamine, are considered to function similarly in balancing the required volatility and hydrophilicity properties of the polymerization inhibitor. Therefore, such phosphate esters and diimines can be advantageously used in cyclic ester polymerization processes to produce polyesters, particularly those in which devolatilization vessels and / or wash sections are employed.

According to another aspect, the present invention refers to a condensed phase composition, which can be obtained with a process as described above and which comprises:

i) at least 95% by weight of cyclic ester,

ii) at least 0.5 ppm of at least one catalyst capable of catalyzing a polymerization of the cyclic ester and / or

at least 0.01 mmol per kg of at least one initiator capable of initiating a polymerization of the cyclic ester and

iii) 0.001 to 0.5% by weight of polymerization inhibitor.

As a polymerization inhibitor, any substance within the scope of the present invention can be used which is capable of inhibiting an oligomerization and / or polymerization of a cyclic ester, particularly in the presence of a catalyst and / or an initiator. Since the amount of polymerization inhibitor to be added to the reaction mixture and / or condensed phase composition decreases with the effectiveness of the polymerization inhibitor, it is preferred to use a strong polymerization inhibitor. In particular, good results are achieved, when the at least one polymerization inhibitor is an imine or a diimine, such as N, N'-bis (salicylidene) -1,3-propanediamine and / or a phosphoric acid derivative, such as a phosphoric acid ester, preferably an alkanoic acid phosphate or an alkoxylated alcohol-based acid phosphate compound, more preferably a stearic acid phosphate compound and most preferably a mono-C4-18 alkyl phosphate ester , a di-C4-18 alkyl phosphate ester or a mixture of monostearic acid phosphate and di-stearic acid phosphate.

According to another aspect, the present invention relates to the use of the aforementioned condensed phase composition for the production of a polyester, in which before the start of the polymerization catalyst and / or polymerization initiator, they are added to the condensed phase composition , so that the total amount of polymerization catalyst is 1 ppm to 1% by weight and / or the total amount of polymerization initiator is 0.1 to 50 mmol / kg based on the total amount of phase composition condensed.

According to another aspect, the present invention relates to the use of the aforementioned condensed phase composition for the production of a polyester, where the condensed phase composition is mixed with a melt comprising a cyclic ester and / or a polyester, with the optional addition of a polymerization catalyst and / or polymerization initiator, so that the total amount of polymerization initiator is 0.1 to 50 mmol / kg by weight based on the total amount of final composition, where the mixture thus obtained, it is then further polymerized.

This embodiment is particularly suitable for the production of polylactic acid.

According to a further embodiment of the present invention, the polymerization inhibitor used in the process is selected from the group consisting of mono or diimines, esters of phosphoric acid, acid phosphates based on alkoxylated alcohol, mono- and / or di-alkyl phosphates, RPO4H2 and / or R2PO4H, where each R is independently a C ^6-16 linear, branched or cyclic alkyl group or a combination thereof.

Due to the reasons stated above, preferably a diimine is used as a polymerization inhibitor, such as N, N'-bis (salicylidene) -1,3-propanediamine, and / or a phosphate ester according to the general formula (I)

where preferably R ', R "and R'" independently have the general structure as in general formula (II)

where i) n> 0 and Q is independently a substituted alkyl group, branched or linear C ^{1 to 16,} and R is independently H or substituted straight chain alkyl group, branched or cyclic or a derivative of the phenyl group or where ii) n = 0 and R is independently a H or a C ^6-16 linear, branched or cyclic substituted alkyl group or a derivative of the phenyl group. Preferably, at least one of R ', R "and R'" is an H in general formula (I).

Preferably, in formula (I) above, i) R 'is an H and R "and R'" are in accordance with general Formula (II) or ii) R 'and R "are an H and R'" are according to the general formula (II).

Furthermore, n is in the general formula (II) preferably greater than 0, more preferably an integer from 2 to 20 and even more preferably an integer from 2 to 11.

According to a particular preferred embodiment, n is in general formula (II) an integer from 2 to 20 and R is an alkyl group. Even more preferable, n is an integer from 2 to 20, R is an alkyl group with less than 16 carbon atoms, and Q is a CH ² -CH ^{2 group} . Therefore, preferred examples are poly (oxy-1,2-ethanediyl), alpha-isotridecyl omega-hydroxy-phosphate (CAS 9046-01-9) and poly (oxy-1,2-ethanediyl), alpha-hydro-omega-hydroxy-mono-Ci ² -i ⁵ -alkyl ether phosphates (CAS 68071 -35-2).

By adding such a preferred kind of polymerization inhibitor to the reaction mixture, the transparency and / or visual appearance of the material is quite good and haze in the polymerization product can often be minimized reliably and surprisingly. Problems related to blockages, phase separations, the generation of sediment from solid by-products and / or scale in the equipment and / or the cleaning of the equipment, in the devolatilization and / or in the washing sections can be minimized. Furthermore, such preferred classes of polymerization inhibitors allow the production of higher viscosity polymers compared to other inhibitors, such as mono and distearyl acid phosphates, which are known in the prior art. Furthermore, it has been found that these polymerization inhibitors can be used in all known conventional processes for adding polymerization inhibitors, such as those known from EP 2698394 A1, WO 2014/027037 A1 or US 5,770,682.

Apart from that, the polymerization inhibitor can generally be a [poly (oxy-1,2-ethanediyl) mono-alkyl ether phosphate], a [poly (oxy-1,2-ethanediol) -phenyl-hydroxy phosphate ] or a [poly (oxy-1,2-ethanediyl) omega-hydroxy phosphate].

Furthermore, it is preferred that the cyclic ester in alternatives ia) and ib) of the process according to the present invention is lactide so that polylactic acid is produced in the process.

Furthermore, it is preferred that the concentration of the compound in the composition is 0.001 to 0.5% by weight and more preferably 0.02 to 0.15% by weight.

Specific embodiments according to the present invention are now described with reference to the accompanying drawings.

Fig. 1 is a schematic drawing of a plant for stabilizing a condensed phase composition in a process for manufacturing polyester from cyclic ester monomer according to a first embodiment of the present invention.

Fig. 2 is a schematic drawing of a plant for stabilizing a condensed phase composition in a process for manufacturing polyester from cyclic ester monomer according to a second embodiment of the present invention.

Fig. 3 is a schematic drawing of a downstream wash section of a plant shown in Fig. 1 or Fig. 2.

Fig. 4 shows the evolution of the monomer content in example 3 through the devolatilization section in two stages in the absence (circles) and in the presence (diamonds) of an alkoxylated alcohol-based acid phosphate.

Figure 1 shows a plant for stabilizing a condensed phase composition in a process for manufacturing a polyester from a cyclic ester monomer according to a first embodiment of the present invention.

The plant comprises a reactor system 10 to polymerize cyclic ester in the presence of a catalyst and optionally an initiator to form a reaction mixture comprising unreacted polyester and cyclic ester, downstream of it a unit 12 and downstream of it a first devolatilization chamber 14. Unit 12 is a static mixer, a heat exchanger, or a combination thereof.

From the top of the first devolatilization chamber 14, a vapor line 16 leads to a condenser 18, comprising a gas extraction line 20 and a fluid extraction line 22. The fluid extraction line 22 leads to a static melt crystallizer 24, which is connected by means of a recycle line 26 with the feed of the reactor system 10. In the recycle line 26, a cyclic ester supply line 28, as well as with a supply line 30 for the polymerization catalyst and polymerization initiator cables. Lines 26, 28 and 30 are combined with feed line 32 leading to reactor system 10.

From the bottom of the first devolatilization chamber 14, a liquid line 34 leads to a unit 36 and from there through line 38 to a second devolatilization chamber 40, where the unit 36 is a static mixer, a heat exchanger or a combination thereof. The second devolatilization chamber 40 comprises a polymer extraction line 42 and a vapor removal line 44.

Three supply lines are provided for the polymerization inhibitor 46, 46 ', 46 "', namely a first 46 leading to the line leading to unit 12, a second 46 'leading to line 34 leading to unit 36 and a third 46 "leading to condenser 18.

Subsequently, the continuous operation of this plant is described by using lactide as a cyclic ester starting material to prepare polylactic acid.

The fresh lactide is supplied through supply line 28 and the new polymerization catalyst, namely tin octoate, and the new polymerization initiator, namely 2-ethylhexanol, are delivered through the line supply line 30 to recycle line 26. The mixture of these streams is fed through supply line 32, which optionally includes a static mixer, into reactor system 10, comprising one or more polymerization reactors and preferably one to three closed loop reactors and optionally at least one plug flow reactor. The mixture polymerizes in reactor system 10 forming a reaction mixture or reaction mixture, respectively, containing polylactic acid having a Mw of at least 20,000 g / mol, unreacted lactide, polymerization catalyst, and polymerization initiator. Through supply line 46, at least one polymerization inhibitor, for example, a mixture of monostearic acid phosphate and di-stearic acid phosphate, is added to this stream and the combined stream is conducted to unit 12, where mix homogeneously.

The mixture thus obtained is transported to the first devolatilization chamber 14, which operates in this case at a temperature of 190 ° C and at a pressure of 15 mbar. Under these conditions, in the devolatilization chamber 14, a vapor stream that mainly includes unreacted lactide and the catalyst and / or the initiator and / or a reaction product or a residue of the at least one catalyst and / or at least one initiator, as well as a liquid stream that includes primarily the polylactic acid product, a portion of the catalyst, a portion of the initiator, and all or at least essentially all of the polymerization inhibitor fed into the stream through the separate phase line 46. The reason that all or at least essentially all of the polymerization inhibitor is included in the liquid stream withdrawn from the first devolatilization chamber 14 through line 34 is that the polymerization inhibitor, i.e. the phosphate mixture of monostearic acid and di-stearic acid phosphate, has under these devolatilization conditions, that is, at a temperature of 190 ° C and a pressure of 15 mbar, a volatility so low that it is not transferred in the devolatilization chamber to the stream of steam. It should be noted that the polymerization inhibitor is added in this case through line 46 not for the purpose of stabilizing the composition of the condensed phase in the stream drawn from reactor system 10, but for the sole purpose of stabilizing the acid product. polylactic, i.e. to avoid further polymerization of the polylactic acid.

Through line 46 'an additional polymerization inhibitor is added to the crude product stream and the mixture thus obtained is transported to unit 36, where it is homogeneously mixed. Subsequently, the crude product is subjected to a second devolatilization in the second devolatilization chamber 40, where residual low-boiling impurities, primarily lactide, are removed from the purified polylactic acid product stream. While the purified polylactic acid product stream is removed from the plant through polymer line 42, residual impurities are removed from the plant through vapor removal line 44. Alternatively, residual impurities, including The lactide can be fed to vapor line 16 or condensed and fed to fluid extraction line 22.

The vapor obtained in the first devolatilization chamber 14 is drawn from the first devolatilization chamber 14 through the vapor line 16 and fed to the condenser 18. In the condenser, a condensed phase enriched with lactide is obtained. In addition, a mixture of monostearic acid phosphate and di-stearic acid phosphate is supplied as a polymerization inhibitor through line 46 "in condenser 18 in the condensed phase composition obtained therein and mixed to obtain a mixture. The condensed phase composition is removed from condenser 18 as a homogeneous mixture and transported through recycle line 26 to static melt crystallizer 24, where the lactide is separated from impurities, i.e., polymerization catalyst remaining, the remaining polymerization initiator and polymerization inhibitor The purified lactide thus obtained is recycled into the reactor system 10 through lines 26.

Due to the addition of the polymerization inhibitor through line 46 "in condenser 18 in the condensed phase composition, this composition is stabilized against oligomerization and / or polymerization initiated by the catalyst and / or initiator included in it, so that the stabilized condensed phase composition can be incubated for a long period of time, that is, in particular for several days, such as for at least 10 days, at elevated temperatures of, for example, 120 ° C, that is , in the molten state, without any oligomerization and / or polymerization of the lactide, which would not only lead to an undesired consumption of the lactide, but in particular also to an undesired increase in the viscosity of the condensed phase composition, which which would make it difficult, if not impossible, to transport the composition from the condensed phase to the crystallizer.

The plant for stabilizing a condensed phase composition in a process for manufacturing polyester from cyclic ester monomer according to a second embodiment of the present invention, as shown in Figure 2, is identical to that of the plant shown in Figure 1 except that the supply line for the 46 "polymerization inhibitor is missing in condenser 18. In this embodiment, more mixture of monostearic acid phosphate and di-stearic acid phosphate is supplied as polymerization inhibitor through the line 46 to the reaction mixture extracted from reaction system 10 and devolatilization is carried out in the first devolatilization chamber at a higher temperature and a lower pressure, that is, at a temperature of 215 ° C at a pressure of 3 mbar For this reason, a sufficient amount of polymerization inhibitor transferred in the vapor phase extracted from the first devolatilization chamber 14 through the line is needed. 16 so that a condensed phase composition is obtained in condenser 18, which is stabilized as well as that obtained with the plant shown in figure 1.

Figure 3 shows a washing section with a recirculation or circulation system, respectively, to remove lactide from the steam extracted from the second devolatilization chamber 40 as stream 44 shown in Figures 1 and 2. Steam stream 44 is passes through a steam ejector 48 and is then fed to a countercurrent column 50, where it is contacted with an aqueous solution, which is distributed at the head of the countercurrent column 50 by means of of a manifold 52. Column 50 is maintained under vacuum by means of vacuum system 54. Lactide in vapor stream 44 dissolves and is at least partially hydrolyzed in the aqueous solution and then removed from the column 50 and is introduced into the recirculation system 56, where it is pumped by means of the pump 58. A partial stream of this mixture is withdrawn from the plant through the extraction line 60 and is removed. The remaining partial stream of the mixture is pumped through a first heat exchanger 64 and a second heat exchanger 66, where it is heated to a temperature suitable for complete or at least nearly complete dissolution or hydrolysis of the lactide, before be transported to reactor 68, where it is incubated for a time sufficient to effect complete or at least almost complete dissolution and hydrolysis of the lactide. The mixture is then pumped through the first heat exchanger 64 and through a third heat exchanger 70, before being fed to the manifold 52.

Alternatively to the embodiment shown in figure 3, the scrubbing section can be connected with the steam 16 extracted from the first devolatilization chamber 14. It can even replace the condenser in this embodiment, or it can be connected with the gas extraction line 20 in addition to capacitor 18.

Also, it will be understood that the scrubbing section for removing lactide from the steam drawn from the second devolatilization chamber 40 may also optionally be used in conjunction with a condenser.

Accordingly, the polymerization inhibitor and / or its decomposition and / or hydrolysis products can often also be detected in the recirculation system 56 for these embodiments having a wash section.

The present invention is described below by way of non-limiting examples.

Example 1

Example 1-1

The lactide was melted and fed together with tin (II) octoate as a catalyst and with 2-ethylhexanol as an initiator into a continuous polymerization reactor, which was composed of a closed loop reactor and a downstream plug flow reactor. , where the lactide was polymerized in the presence of the catalyst and the initiator. At the end of the polymerization reactor, the content of unreacted lactide in the reaction mixture was 4 to 6% by weight.

Then 0.15 to 0.2% by weight of a molten phosphorus compound available as commercial product ADK STAB AX-71 from Adeka Palmarole company, which is a mixture of mono and distearyl acid phosphate, were added as polymerization inhibitor to the reaction mixture as a side flow and mixed with indication mixers. To remove the unreacted lactide, the reaction mixture thus obtained was subjected to devolatilization in a devolatilization apparatus as described in US 7,942,955 B2 at a temperature of 224 ° C and a pressure of 4.9 mbar, where An unreacted lactide-enriched fraction was obtained as a vapor stream and a polymer-rich phase was obtained as a molten residue. The vapor stream was then condensed into a condensed phase and collected in a hot tank connected to a vapor outlet line from the devolatilization vessel. The hot tank was adjusted to a temperature of 100 to 105 ° C.

Subsequently, the phosphorus content in the condensed phase composition was measured by 31P-NMR and by ICP-MS. Consequently, the condensed phase contained 34 ppm of phosphorus.

This example shows that when carrying out devolatilization of a composition that includes unreacted lactide and the phosphorus compound ADK STAB AX-71 as a polymerization inhibitor at a temperature of 224 ° C and a pressure of 4.9 mbar, a quantity is transferred measurable amount of polymerization inhibitor in the condensed phase.

Example 1-2

The polymer-rich molten residue obtained after devolatilization in Example 1-1 was subjected to further devolatilization, which was carried out at a temperature of 225 ° C and a pressure of 1.0 mbar. The resulting vapor stream was condensed and the condensed phase thus obtained was analyzed for phosphorus content by 31P-NMR and by ICP-MS.

Consequently, the condensed phase contained 260 ppm phosphorus.

This example shows that when carrying out devolatilization of a composition that includes unreacted lactide and the phosphorus compound ADK STAB AX-71 as a polymerization inhibitor at a temperature of 225 ° C and a pressure of 1.0 mbar, a quantity is transferred measurable amount of polymerization inhibitor in the condensed phase.

Comparative Example 1

Comparative Example 1-1

Example 1 -1 was repeated, except that devolatilization was carried out at a temperature of 203 ° C and at a pressure of 4.0 mbar. The resulting vapor stream was condensed and the condensed phase thus obtained was analyzed for phosphorus content by 31P-NMR and by ICP-MS.

Consequently, the condensed phase did not contain measurable amounts of the phosphorus compound.

Comparative Example 1-2

Example 1 -1 was repeated, except that devolatilization was carried out at a temperature of 199 ° C and a pressure of 3.1 mbar. The resulting vapor stream was condensed and the condensed phase thus obtained was analyzed for phosphorus content by 31P-NMR and by ICP-MS.

Consequently, the condensed phase did not contain measurable amounts of the phosphorus compound.

Comparative Examples 1-1 and 1-2 show that when performing devolatilization of a composition including unreacted lactide and the phosphorus compound ADK STAB AX-71 as a polymerization inhibitor at a temperature of about 200 ° C and at a pressure at about 3 to 4 mbar, no measurable amount of polymerization inhibitor is transferred to the condensed phase.

Example 2

Example 2-1

The lactide was melted and fed together with 100 ppm of tin (II) octoate as catalyst and with 20 mmol of 2-ethylhexanol initiator as initiator per kg of lactide into a continuous polymerization reactor, which was composed of a reactor of closed loop and a downstream plug flow reactor, where the lactide was polymerized in the presence of the catalyst and initiator. At the end of the polymerization reactor, the content of unreacted lactide in the reaction mixture was 4% by weight.

Next, 0.15 to 0.2% by weight of a molten phosphorus compound available as commercial product ADK STAB AX-71 from the Adeka Palmarole company was added as a polymerization inhibitor to the reaction mixture as a side stream and they were mixed using reaction mixers. To remove unreacted lactide, the reaction mixture thus obtained was subjected to devolatilization in a devolatilization apparatus as described in US 7,942,955 B2 at a temperature of 224 ° C and a pressure of about 4.0 ± 1 0 mbar, in which a fraction enriched with unreacted lactide was obtained as a vapor stream and a polymer-rich phase was obtained as a molten residue. The vapor stream was then condensed into a condensed phase and collected in a hot tank connected to a vapor outlet line from the devolatilization vessel. The hot tank was adjusted to a temperature of 100 to 105 ° C.

Subsequently, the stability of the condensed phase was evaluated by determining the degree of conversion of the polymerizable cyclic ester included in the condensed phase after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as initiator of the composition. of the condensed phase and a subsequent heat treatment of the condensed phase under inert atmosphere conditions for 12 hours at 160 ° C. The degree of conversion of the polymerizable cyclic ester in the composition of the condensed phase was calculated as 100 ■ (c ⁰ - Cf) / Cü, where c ⁰ is the initial concentration of the cyclic ester in the composition of the condensed phase obtained by the condensation of the vapor stream and cf is the concentration of the cyclic ester in the condensed phase composition after the aforementioned heat treatment. Both concentrations c ⁰ and Cf were measured with gas chromatography.

The degree of conversion of the polymerizable cyclic ester in the condensed phase was less than 5% by weight.

This example shows that by adding a polymerization inhibitor to the reaction mixture and performing devolatilization of the composition thus obtained including unreacted lactide, catalyst, polymerization initiator and the phosphorus compound ADK STAB AX-71 as polymerization inhibitor at a temperature of 224 ° C and at a pressure of approximately 4.0 mbar, before the vapor stream obtained condenses, a stable condensed phase is obtained because a measurable amount of the polymerization inhibitor is transferred to the condensed phase and protects the lactide unreacted from being polymerized.

Example 2-2

An aliquot of the condensed phase obtained after condensation in Example 2-1 was purified by crystallization.

More specifically, a glass vial was filled with 9.6 g of the condensed phase and then sealed. The composition was melted in a furnace at 120 ° C and then subjected to a first crystallization stage by cooling it to 90 ° C. After 20 h, an amount equal to 8.5 g corresponding to a weight fraction of 88.5% of the initial stabilized composition solidified into a solid crystalline fraction C1, while the remaining 1.1 g corresponding to a fraction by weight 11.5% of the initial composition remained a liquid fraction L1.

After removing the liquid fraction L1 from the glass vial, the vial was sealed again and the solid fraction C1 was subjected to a second purification step by first melting the fraction C1 and then cooling it at 95 ° C for 3 h, then at 90 ° C for 18h and finally at 85 ° C for 7h. At the end of this second purification step, the composition phase separated into a liquid phase L2 (11.3% by weight) and a solid crystalline phase C2 (88.7% by weight).

The phosphorus content was measured for each phase.

While the solid crystalline fraction C1 obtained after the first stage of crystallization contained 20 ppm of phosphorus and the solid crystalline fraction C2 obtained after the second stage of crystallization contained 13 ppm of phosphorus, the liquid fraction L1 obtained after the first stage crystallization contained 115 ppm of phosphorus and the liquid fraction L2 obtained after the second crystallization stage contained 86 ppm of phosphorus.

These results show that the polymerization inhibitor can be substantially removed from the condensed phase by crystallization.

Comparative example 2

Comparative Example 2-1

Example 2-1 was repeated except that devolatilization was carried out at a temperature of 204 ° C and a pressure of 4.0 mbar and except that no polymerization inhibitor was added.

The degree of conversion of the polymerizable cyclic ester in the condensed phase was 78.2 ± 0.6% by weight.

This comparative example shows that a condensed phase obtained by devolatilizing a reaction mixture containing polymerizable cyclic ester, polymerization catalyst, and polymerization initiator, and then condensing the vapor phase obtained in devolatilization, without adding any polymerization inhibitor to the composition is not stable, but polymerizes at significantly elevated temperatures.

Comparative Example 2-2

Example 2-1 was repeated, except that devolatilization was carried out at a temperature of 203 ° C and a pressure of 4.0 mbar.

The degree of conversion of the polymerizable cyclic ester in the condensed phase was 50.7 ± 3.3% by weight.

This comparative example shows that a condensed phase obtained by devolatilizing a reaction mixture containing polymerizable cyclic ester, polymerization catalyst, a polymerization initiator and polymerization inhibitor at a temperature of approximately 200 ° C and a pressure of approximately 4 mbar and Then, by condensing, the vapor phase that is obtained in devolatilization is not stable, but it polymerizes at significantly high temperatures.

Example 3

A plant as shown in figure 1 was operated with lactide as the cyclic ester. Poly (oxy-1,2-ethanediyl), alpha - hydroxy-omega-hydroxy-mono-C ^12-15 -alkyl ether phosphate (CAS No.: 68071-35-2) was used as a polymerization inhibitor was added to the polymerization stream at the outlet of the loop and plug flow reactor 10 at position 46. Three runs were run over several days of continuous operation, where the inhibitor concentrations were 0.04% by weight, 0, 05% by weight and 0.1% by weight, respectively, with respect to the lactide fed to the polymerization reactor. A scrubbing system as shown in Figure 3 was in fluid connection with the steam stream 44 drawn from the outlet of the second devolatilizer 40. The polymerization plant was kept in operation for several days in the rough and the appearance of scale was controlled. continuously during plant operation.

No evidence of solid deposits could be seen in either the countercurrent column 50 or the recirculation system 56.

For each of the three runs, during plant operation, the polylactic acid product in the removal line 42 of the polymerization plant was granulated using a conventional underwater granulator and pellet samples in the size range mm were collected. for characterization. The results obtained are summarized in Tables 1 and 2.

Table 1. Results of the characterization of the polylactide tablets (PLA).

Table 2. Characterization results of PLA tablets.

The results summarized in Table 1 show that a low residual monomer PLA with high stability against lactide reform is obtained according to the present invention. The residual monomer was consistently less than 0.3% by weight and even less than 0.2%. Lactide reform was consistently less than 0.3%.

Furthermore, the results summarized in Table 2 show that all samples had an extremely good visual appearance. While an acceptable value of the yellowness index is YI <30, and is preferably less than YI <20, an even lower yellowness index was recorded in the examples, that is, one that was consistently less than 10 and even less than 3 after crystallization of the tablets. Similarly, for haze, H was below H <10 and constantly below H <3.

The residual monomer content of lactide was measured by gas chromatography (GC). A sample was dissolved in a dichloromethane along with 1-octanol as an internal standard. The polymer was precipitated from solution by mixing 1 ml of solution with 10 ml of an antisolvent solution, specifically a mixture of acetone / hexane (5/95 vol / vol). The final solution was stirred for 1 to 2 hours to ensure complete precipitation of the polymer and the supernatant of the final solution thus obtained was filtered and injected into the GC.

The yellowness index was measured using a chromameter as follows: a Petri dish was filled with 15 g of PLA tablets and the yellowness index, YI, was measured according to the ASTM D1925 procedure, with illuminant C and 2nd observer.

Lactide reform was measured as follows: First, the residual lactide monomer content in the sample was measured by gas chromatography and quantified as weight percent of lactide in the sample, RM1. The sample tablets were then dried for at least 4 hours in an inert atmosphere at 70 ° C, loaded into a melt flow index instrument and heated in the MFI capillary at the desired temperature for a time equal to the time test. After the test time passed, the material was withdrawn from the MFI outlet as a thin strand, the lactide content of which was again measured by GC, RM2. The extent of lactide reform was then measured as ARM = RM2-RM1 which measured the amount of lactide reformed during the test.

Transmission haze was measured on the Haze-Gard Plus® apparatus (BYK Gardner GmbH, Germany) according to ASTM D 1003 (ISO / DIS 14782). Haze transmission (Haze) is defined as:

where Tdif is the diffuse transmittance and Tt is the total transmittance. Haze was measured at 10 different positions on the samples to verify the uniformity of the sample. The samples were prepared as follows: PLA tablets were dried at 80 ° C for 4 hours under nitrogen flow. The tablets were then molded into 3x2x0.5 cm plates using a press heated to 200 ° C, which was rapidly cooled with a water-cooled press after the tablets were melted. Samples free of defects (e.g., bubbles) were pressed to then into 1mm thick films using the same pressing system and then used for measurement.

Figure 4 shows the evolution of the monomer content through the two-stage devolatilization section in the absence and in the presence of poly (oxy-1,2-ethanediyl), alpha-hydroxy-omega-hydroxy-mono-C12-15 -alkyl ether phosphate (CAS No: 68071-35-2). The dashed line represents the maximum tolerated value to produce an industrially relevant material. The solid lines are provided as a guide to the eye. This figure demonstrates the additional benefit of using an alkoxylated alcohol-based acid phosphate as a polymerization inhibitor in terms of minimizing undesirable loss of monomer in the upper devolatilization system. Without wishing to be limited by a specific mechanism, the inventors believe that this shows that such polymerization inhibitors are effective in minimizing unwanted depolymerization reactions and other chain depolymerization reactions that would release the monomer resulting in its unwanted loss through subsequent devolatilization. Therefore, in preferred embodiments of the invention, the addition of an alkoxylated alcohol-based acid phosphate as a polymerization inhibitor will substantially decrease the amount of devolatilized monomer to the upper system compared to the case where no inhibitor is added. polymerization. One skilled in the art will understand that this difference can be measured and expressed as a flow rate to the upper system (e.g., kg / h, measured by accumulating devolatilized mass over a defined period of time) or as a relative percentage of the advancement of the feed flow into the devolatilization system. In some specific preferred embodiments, the monomer content going to a first devolatilization unit will be reduced by at least 0.5% and to a second devolatilization unit by at least 1, preferably 2%, all relative to the stream of feeding. It was also observed (not shown) that the use of the alkoxylated alcohol-based acid phosphate polymerization inhibitors, specifically poly (oxy-1,2-ethanediyl), alpha-hydroxy-omega-hydroxy-mono-C12 -15-alkyl ether phosphate (CAS No: 68071-35-2), also significantly reduced the yellowness index of the polymer samples taken after either of the two devolatilization units compared to the comparative examples in which no polymerization inhibitor was added. Therefore, in preferred embodiments of the invention, the addition of an alkoxylated alcohol-based acid phosphate as a polymerization inhibitor will substantially decrease the yellowness number of the polymer mass exiting the unit (s). of devolatilization versus the case in which no polymerization inhibitor is added. In certain specific preferred embodiments of the invention, the use of these polymerization inhibitors has been found to reduce the yellowness index of the final polymer pellets by at least 5, preferably 10, as measured according to YI-D1925.

Comparative Example 3-1

The same procedure as in Example 3 was repeated, except that a mixture of mono and di-stearic acid phosphates was added to the polymerization stream at position 46 so that the inhibitor concentration was 0.1% by weight.

Extensive fouling was observed in the wash system. More specifically, the scale was in the form of waxy debris floating in the liquid solution in countercurrent column 50, which in turn caused difficult operation of recirculation system 56.

This example clearly demonstrates that not all phosphorous-based compounds can be used in a polymerization plant for the production of polylactic acid.

Comparative Example 3-2

The same procedure as in Comparative Example 3-1 was repeated, except that dibutyl phosphate was added to the polymerization stream at position 46. Two cycles were run, one first with an inhibitor concentration of 0.1% by weight. and a second with an inhibitor concentration of 0.04% by weight with respect to the lactide feed.

In both runs, after a few hours of dosing the inhibitor, it was possible to observe through the glass window present in the devolatilization container 14 that layers of material began to deposit on the walls of the devolatilizer, as well as on the window of glass. Due to the high temperature of the devolatilizer, this layer of material became black charred layers.

A similar phenomenon was observed in a separate run in which dibutyl phosphate was added to the polymerization stream at position 46 ', causing deposition of material on the glass window and walls of devolatilizer 40. Also this Comparative example clearly shows that not all phosphorus-based compounds can be used in a polymerization plant for the production of polylactic acid.

Example 4 and comparative example 4

Solutions were prepared by mixing 5 ml of lactic acid and 5 ml of water in a vial along with a weighted amount of inhibitor as reported in Table 3.

All vials were sealed immediately after preparing the solutions. The physical state of each additive, in its pure state at room temperature, is reported in the third column of Table 3.

The solutions were then stirred for / hour and allowed to rest for a few hours. The physical state of the solutions was then observed. All but the solution containing ADK-AX-71 were composed of free flowing liquid, e.g. For example, they apparently did not have any solid residue or solid insoluble fraction. To verify whether the presence of suspended material in the solution containing ADK-AX-71 was due to slow solubilization or a real insolubility problem, all solutions were further heated in an oven at 130 ° C for 2 hours to ensure a complete melting of inhibitors and then allowed to cool to room temperature.

The presence or absence of insoluble fractions is reported in Table 3.

Table 3. Inhibitor solubility test

Example 5

A 20 ml vial was filled with 5 g of lactide and 0.19% by weight of N, N'-bis (salicylidene) -1,3-propanediamine. The vial was placed in the oven at 80 ° C for 5 hours to dry the lactide. After drying, the vial was sealed and heated to 160 ° C to melt the lactide. Next, a 0.1 ml solution of a 1% (w / w) solution of tin octoate / ethyl-hexanol was injected into the vial, which was shaken to homogenize the mixture and allowed to react overnight. The same procedure was applied to a second vial without adding any inhibitor.

After the reaction, both vials were cooled and their contents were analyzed by gas chromatography. The procedure thus described was repeated twice with the inhibitor and twice without the inhibitor, to ensure reproducibility. The results below are the average of the two repetitions.

An average lactide conversion of 72% was measured for the polymerized sample in the absence of N, N'-bis (salicylidene) -1,3-propanediamine, while a negligible average conversion of much less than 5% was measured in the presence of N, N'-bis (salicylidene) -1,3-propanediamine.

These results show that N, N'-bis (salicylidene) -1,3-propanediamine is a very effective catalyst inhibitor, which, as shown in the example above, is not expected to cause any fouling problems in a catalyst system. washing as shown in figure 3.

Reference numbers

10 reactor system

12 unit (mixer (s) and / or heat exchangers)

14 first devolatilization chamber

16 steam line

18 capacitor

gas extraction line

fluid extraction line

static melting crystallizer

recycling line

cyclic ester supply line (lactide)

supply line for catalyst and initiator

supply line

liquid line (molten)

unit (mixer (s) and / or heat exchangers)

line

second devolatilization chamber

polymer extraction line

vapor removal line

, 46 ', 46 "supply line for ejector polymerization inhibitor (s)

countercurrent column

distributor for aqueous solution

vacuum system

recirculation system

bomb

extraction line

line

first heat exchanger

second heat exchanger

reactor

third heat exchanger

Claims (12)

1. A process for stabilizing a condensed phase composition, containing i) at least one polymerizable cyclic ester and ii) at least one catalyst capable of catalyzing a polymerization of the cyclic ester and / or at least one initiator capable of initiating a polymerization of the cycle ester and / or a reaction product or a residue of the at least one catalyst and / or of the at least one initiator, i) where the process is used in a process for manufacturing a polyester from a cyclic ester monomer and comprises the steps of: a) provide a cyclic ester, b) polymerizing the cyclic ester in the presence of the catalyst and optionally the initiator in a reactor to form a reaction mixture comprising unreacted polyester and cyclic ester, c) subjecting the reaction mixture to devolatilization to obtain a purified polyester as a molten residue and a vapor, which mainly includes i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and / or the at least one initiator and / or a reaction product or a residue of the at least one catalyst and / or the at least one initiator, and d) subjecting the vapor stream to condensation to obtain the composition of the condensed phase, where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture and / or to the composition of the condensed phase in an amount such that the degree of conversion of the polymerizable cyclic ester in the composition of the condensed phase is not more than 15 %, where degree of conversion is 100 ■ (c ⁰ - Cf) / C ⁰ , where c ⁰ is the initial concentration of the cyclic ester in the condensed phase composition obtained by the condensation of the vapor stream and cf is the concentration of the cyclic ester in the composition of the condensed phase after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as initiator of the composition of the condensed phase and a subsequent heat treatment of the condensed phase under conditions inert atmosphere for 12 hours at 160 ° C, where ia) at least a part of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition, and / or ib) at least a part of the polymerization inhibitor is added to the reaction mixture before step c), and where devolatilization is carried out at a temperature higher than 203 ° C and a pressure lower than 4 mbar or, alternatively , at a temperature above 220 ° C and at a pressure below 5 mbar, or ii) where the process is used in a lactide manufacturing process from lactic acid and comprises the steps of: a) provide lactic acid, b) polycondensation of lactic acid in a reactor to form a reaction mixture comprising a polylactic acid prepolymer, c) adding a catalyst to the reaction mixture and depolymerizing the reaction mixture, d) devolatilizing the reaction mixture to obtain a crude lactide stream, e) subjecting the vapor stream to condensation to obtain the condensed phase composition, where at least one polymerization inhibitor is added as a stabilizer to the reaction mixture and / or to the composition of the condensed phase in an amount such that the degree of conversion of the polymerizable cyclic ester in the composition of the condensed phase is not more than 15 %, where degree of conversion is 100 ■ (c ⁰ - Cf) / Cü, where c ⁰ is the initial concentration of the cyclic ester in the condensed phase composition obtained by condensation of the vapor stream and cf is the concentration of the ester cyclic in the composition of the condensed phase after the addition of 150 ppm of tin octoate as catalyst and of 100 mmol / kg of ethylhexanol as initiator of the composition of the condensed phase and a subsequent heat treatment of the condensed phase under conditions of inert atmosphere for 12 hours at 16 ° C, where at least a part of the polymerization inhibitor is added to the vapor stream extracted from devolatilization and / or to the condensed composition. The process according to claim 1, wherein the degree of conversion of the polymerizable cyclic ester in the condensed phase composition is not more than 10%, preferably not more than 5%, more preferably not more than 2%, even more preferably not more than 1%, and even more preferably not more than 0.1%. The process according to claim 1 or 2, wherein the at least one cyclic ester in alternative i) is selected from the group consisting of lactide, L-lactide, D-lactide, meso-lactide, £ -caprolactone, glycolide or mixtures of one or more of the substances mentioned above. The process according to any of the preceding claims, wherein the reaction mixture and the condensed phase composition each contain as a catalyst at least one organometallic compound comprising a metal selected from the group consisting of magnesium, titanium, zinc, aluminum, indium, yttrium, tin, lead, antimony, bismuth and any combination of two or more of the metals mentioned above, wherein the at least one organometallic compound preferably comprises as an organic residue a residue selected from the group consisting of alkyl groups, aryl groups, halides, oxides, alkanoates, alkoxides and any combination of two or more of the groups mentioned above. 5. The process according to any of the preceding claims, wherein the reaction mixture and the condensed phase composition each contain as initiator at least one compound comprising at least one carboxyl group and / or hydroxyl group and preferably at least one selected compound from the group consisting of water, alcohols, lactic acid, cyclic ester oligomers, cyclic ester polymers, and any combination of two or more of the aforementioned substances. 6. The process according to any of the preceding claims, wherein the at least one polymerization inhibitor is an imine or a diimine, preferably obtained by condensation of aliphatic or aromatic mono or diamines with derivatives of salicylaldehyde and / or a derivative of phosphoric acid. , such as a phosphoric acid ester, preferably N, N'-bis (salicylidene) -1,3-propanediamine, an alkanoic acid phosphate or an alkoxylated alcohol-based acid phosphate compound, more preferably a phosphate compound of stearic acid and most preferably a mono-C ^4-18 alkyl phosphate ester, a di-C ^4-18 alkyl phosphate ester or a mixture of monostearic acid phosphate and di-stearic acid phosphate. 7. The process according to claim 1, wherein the condensed phase composition comprising the polymerization inhibitor is subjected to a purification step, preferably a distillation step or solvent crystallization step and more preferably to a crystallization step in the state molten, to obtain a purified condensed phase composition. 8. The process according to claim 7, wherein the purified cyclic ester is recycled in alternative i) in the reactor. The process according to any of the preceding claims, wherein the condensed phase composition is mixed to homogeneously distribute the polymerization inhibitor. 10. A condensed phase composition obtainable with a process according to any of the preceding claims, wherein the condensed phase composition comprises: i) at least 95% by weight of cyclic ester, ii) at least 0.5 ppm of at least one catalyst capable of catalyzing a polymerization of the cyclic ester and / or at least 0.01 mmol per kg of at least one initiator capable of initiating a polymerization of the cyclic ester and iii) 0.001 to 0.5% by weight of polymerization inhibitor. 11. Use of a condensed phase composition according to claim 10 for the production of a polyester, where before the start of the polymerization catalyst and / or polymerization initiator they are added to the condensed phase composition, so that the total amount of polymerization catalyst is 1 ppm to 1% by weight and / or the total amount of polymerization initiator is 0.1 to 50 mmol / kg based on the total amount of condensed phase composition. 12. Use of a condensed phase composition according to claims 10 for the production of a polyester, wherein the condensed phase composition is mixed with a melt comprising a cyclic ester and / or a polyester, with the optional addition of a catalyst polymerization and / or a polymerization initiator, so that the total amount of polymerization initiator is 0.1 to 50 mmol / kg by weight based on the total amount of final composition, where the mixture thus obtained is further polymerized .